The present invention relates to an optical apparatus and a laser display apparatus each having a laser beam scanner.
Today, devices and apparatuses handling laser beams are required to comply with rigorous safety standards. The equipment utilizing laser beams includes light show devices and bar code readers used by POS (point of sale) systems. Each of these devices is furnished illustratively with a scanner for scanning a target area with a laser beam.
Another typical laser beam device is a display apparatus as part of theater-use projection equipment for projecting images to be viewed by a large audience. In order to acquire a brightly projected image on a large screen, the display apparatus first forms a one-dimensional optical image using one-dimensional light modulators and then causes the optical image thus formed to be scanned perpendicularly for projection, whereby a two-dimensional optical image is projected.
Where the one-dimensional optical image is scanned so as to acquire the two-dimensional projected image, a high-powered laser beam is directed at the screen. Because this laser beam is emitted externally, it is subject to strict safety standards.
In display apparatuses such as scanner-equipped projectors, the scanner could be stopped for some reason. In such a case, the dose of the laser beam per unit projected area could largely exceed normal levels, posing a threat to safety.
Laser scanner-equipped projection display apparatuses designed for higher safety have been proposed. One such apparatus is disclosed illustratively in Japanese Patent Laid-open No. 2000-194302 (as claimed in claim 3 and described in particular in Paragraph p.20, 1.24 to p.21, 1.15).
The projection display apparatus proposed by the above-cited patent application detects the scan timing of the scanner during operation. If the detected timing is found to deviate from reference timing, scanning with the laser beam is stopped. It should be noted that the preferred scanning means for the proposed apparatus is a polygon scanner that rotates at a constant velocity.
There also exist optical and display apparatuses which utilize galvanometer scanners. Unlike polygon mirrors rotating at a constant speed in a fixed direction, the galvanometer scanner makes a reciprocal rotary motion that has a predetermined amplitude, a constant cycle, and a fixed rotation pattern but not a steady speed.
The present invention has been made in view of the above circumstances and provides a laser display apparatus having a scanning safeguard system. This system stops laser beam emission upon detection of a scanner being stopped abnormally for whatever reason, so that the dose of the laser beam will not exceed safety standards. The inventive safeguard system works not only with the polygon mirror setup where the scanner (i.e., mirror) rotates at a constant speed, but also with the galvanometer mirror arrangement in which the mirror moves in reciprocating motion for scan.